Annual report pursuant to Section 13 and 15(d)

Stockholders' equity - Stock Option Activity (Details)

v3.19.1
Stockholders' equity - Stock Option Activity (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Exercise Price Per Share [Abstract]    
Granted, Exercise Price Lower Range Limit (usd per share) $ 2.30  
Granted, Exercise Price Upper Range Limit (usd per share) $ 4.04  
Tecogen    
Stock Options Outstanding [Roll Forward]    
Beginning (shares) 1,061,552  
Granted (shares) 367,500 45,000
Exercised (shares) (57,854) (156,124)
Canceled and forfeited (shares) (78,609)  
Ending (shares) 1,292,589 1,061,552
Exercisable (shares) 855,089  
Vested and expected to vest (shares) 1,226,964  
Weighted Average Exercise Price [Roll Forward]    
Beginning (usd per share) $ 3.60  
Granted (usd per share) 3.35  
Exercised (usd per share) 1.26  
Canceled and forfeited (usd per share) 6.43  
Ending (usd per share) $ 3.52 $ 3.60
Exercised, aggregate intrinsic value $ 137,085 $ 149,598
Exercisable (usd per share) $ 3.46  
Vested and expected to vest (usd per share) $ 3.51  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Outstanding, Aggregate Intrinsic Value $ 671,331 $ 291,449
Exercisable, Aggregate Intrinsic Value 620,266  
Vested and expected to vest, Aggregate Intrinsic Value $ 663,672  
Exercise Price Per Share [Abstract]    
Outstanding, Exercise Price Lower Range Limit (usd per share) $ 0.79 $ 0.79
Outstanding, Exercise Price Upper Range Limit (usd per share) 10.33 18.15
Granted, Exercise Price Lower Range Limit (usd per share) 2.30 3.22
Granted, Exercise Price Upper Range Limit (usd per share) 4.04 $ 3.72
Exercised, Exercise Price Range, Lower Range Limit (usd per share) 1.20  
Exercised, Exercise Price Range, Upper Range Limit (usd per share) 2.60  
Canceled and Forfeited, Exercise Price Lower Range Limit (usd per share) 2.30  
Canceled and Forfeited, Exercise Price Upper Range Limit (usd per share) $ 18.15  
Stock Options | Tecogen    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]    
Outstanding, Weighted Average Remaining Life 5 years 11 months 5 days 4 years 11 months 12 days